U.S. patent application number 17/734116 was filed with the patent office on 2022-08-18 for connection establishment for ue-to-ue relay.
The applicant listed for this patent is Media Tek Singapore Pte. Ltd.. Invention is credited to Guillaume Sebire, Nathan Edward Tenny, Xuelong Wang.
Application Number | 20220264676 17/734116 |
Document ID | / |
Family ID | |
Filed Date | 2022-08-18 |
United States Patent
Application |
20220264676 |
Kind Code |
A1 |
Tenny; Nathan Edward ; et
al. |
August 18, 2022 |
Connection Establishment for UE-to-UE Relay
Abstract
A method of connection establishment for UE-to-UE relay in a
cellular communication system is proposed. A sidelink interface is
used for two remote UEs to communicate directly with a relay UE,
and in which the relay UE forwards communications between the
remote UEs to allow end-to-end communication between the remote
UEs. In one embodiment, a first remote UE initiates a single Direct
Communication (DC) Request that triggers the establishment of
multiple connections between the first remote UE and the relay UE,
and between a second remote UE and the relay UE, such that
end-to-end relayed transport is available between the first and
second remote UE, with hop-by-hop security. The first and second
remote UE can make use of the end-to-end relayed transport to
authenticate and establish end-to-end secured connection.
Inventors: |
Tenny; Nathan Edward; (San
Jose, CA) ; Sebire; Guillaume; (Oulu, FI) ;
Wang; Xuelong; (Beijing, CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Media Tek Singapore Pte. Ltd. |
Singapore |
|
SG |
|
|
Appl. No.: |
17/734116 |
Filed: |
May 2, 2022 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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PCT/CN2021/074338 |
Jan 29, 2021 |
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17734116 |
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International
Class: |
H04W 76/14 20060101
H04W076/14; H04W 12/065 20060101 H04W012/065 |
Claims
1. A method comprising: receiving a first communication request
message from a first remote user equipment (UE) by a relay UE,
wherein the relay UE offers relay service between the first remote
UE and a second remote UE; sending a first response message to the
first remote UE and thereby establishing a first connection of a
first protocol layer with the first remote UE; sending a second
communication request message to a second remote UE in response to
the receiving the first communication request message; receiving a
second response message from the second remote UE and thereby
establishing a second connection of the first protocol layer with
the second remote UE; receiving at least one transmission on the
second connection from the second remote UE; and forwarding the at
least one transmission to the first remote UE on the first
connection.
2. The method of claim 1, further comprising: configuring the first
remote UE with a first configuration of a second protocol layer;
and configuring the second remote UE with a second configuration of
the second protocol layer.
3. The method of claim 2, wherein the configuring the first UE and
the second UE involves using the first protocol layer.
4. The method of claim 1, wherein the establishment of the first
connection comprises: performing a first authentication operation
with the first remote UE; and establishing a first security
relationship with the first remote UE and the sending the first
response message to the first remote UE.
5. The method of claim 1, wherein the establishment of the second
connection comprises: performing a second authentication operation
with the second remote UE; and establishing a second security
relationship with the second remote UE and the receiving the second
response message from the second remote UE.
6. The method of claim 4, wherein the sending the first response
message occurs after the receiving the second response message.
7. The method of claim 4, wherein the performing the first
authentication operation occurs after the receiving the second
response message.
8. The method of claim 1, wherein the first communication request
message is addressed to a broadcast address, or is addressed to an
address of the second remote UE.
9. A method comprising: sending a first communication request
message by a first remote user equipment (UE) to a relay UE that
offers relay service between the remote UE and a second remote UE;
receiving a first response message from the relay UE and thereby
establishing a first connection of a first protocol layer with the
relay UE; communicating with the second remote UE via the relay UE;
receiving a second response message from the second remote UE,
wherein the second response message is triggered by and in response
to the first communication request message via the relay UE; and
establishing a second connection of the first protocol layer with
the second remote UE.
10. The method of claim 9, wherein the establishing of the first
connection comprises: performing a first authentication with the
relay UE; and establishing a first security relationship with the
relay UE and the receiving the first response message from the
relay UE.
11. The method of claim 9, wherein the establishing of the second
connection comprises: performing a second authentication with the
second remote UE; and establishing a second security relationship
with the second remote UE and the receiving the second response
message from the second remote UE.
12. The method of claim 9, further comprising: receiving a
configuration of a second protocol layer from the relay UE;
applying the configuration of the second protocol layer; and
communicating with the second remote UE according to the
configuration of the second protocol layer.
13. The method of claim 9, wherein the first communication request
message is addressed to a broadcast address, or is addressed to an
address of the second remote UE.
14. The method of claim 9, wherein the first remote UE sends a
configuration message using the first protocol layer to the relay
UE over the first connection.
15. The method of claim 9, wherein the first remote UE sends a
configuration message using the first protocol layer to the second
remote UE over the second connection.
16. A Remote User Equipment (UE) comprising: a transmitter that
sends a first communication request message to a relay UE that
offers relay service between the remote UE and a second remote UE;
a receiver that receives a first response message from the relay UE
and thereby establishing a first connection of a first protocol
layer with the relay UE, wherein the remote UE communicates with
the second remote UE via the relay UE; and a connection handling
circuit that establishes a second connection of the first protocol
layer with the second remote UE upon receiving a second response
message from the second remote UE, wherein the second response
message is triggered by and in response to the first communication
request message via the relay UE.
17. The remote UE of claim 16, wherein the remote UE establishes
the first connection upon performing a first authentication with
the relay UE, establishing a first security relationship with the
relay UE, and receiving the first response message.
18. The remote UE of claim 16, wherein the remote UE establishes
the second connection upon performing a second authentication with
the second remote UE, establishing a second security relationship
with the second remote UE, and receiving the second response
message.
19. The remote UE of claim 16, wherein the remote UE receives a
configuration of a second protocol layer from the relay UE, applies
the configuration of the second protocol layer, and communicates
with the second remote UE according to the configuration of the
second protocol layer.
20. The remote UE of claim 16, wherein the first communication
request message is addressed to a broadcast address, or is
addressed to an address of the second remote UE.
21. The remote UE of claim 16, wherein the remote UE sends a
configuration message using the first protocol layer to the relay
UE over the first connection.
22. The remote UE of claim 16, wherein the remote UE sends a
configuration message using the first protocol layer to the second
remote UE over the second connection.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is filed under 35 U.S.C. .sctn. 111(a) and
is based on and hereby claims priority under 35 U.S.C. .sctn. 120
and .sctn. 365(c) from International Application No.
PCT/CN2021/074338, with an international filing date of Jan. 29,
2021, which in turn claims priority from International Application
No. PCT/CN2020/074177, entitled "Connection establishment for a
UE-to-UE relay," filed on Feb. 3, 2020. This application is a
continuation of International Application No. PCT/CN2021/074338,
which claims priority from International Application No.
PCT/CN2020/074177. International Application No. PCT/CN2021/074338
is pending as of the filing date of this application, and the
United States is a designated state in International Application
No. PCT/CN2021/074338. The disclosure of each of the foregoing
documents is incorporated herein by reference.
TECHNICAL FIELD
[0002] The disclosed embodiments relate generally to wireless
network communications, and, more particularly, to UE-to-UE
sidelink relaying in 5G new radio (NR) wireless communications
systems.
BACKGROUND
[0003] In 3GPP LTE cellular networks, an evolved universal
terrestrial radio access network (E-UTRAN) includes a plurality of
base stations, e.g., evolved Node-Bs (eNodeBs or eNBs)
communicating with a plurality of mobile stations referred as user
equipment (UEs). New technologies in 5G new radio (NR) allow
cellular devices to connect directly to one another using a
technique called sidelink communications. Sidelink is the new
communication paradigm in which cellular devices are able to
communicate without their data via the network. The sidelink
interface may also be referred to as a PC5 interface. A variety of
applications may rely on communication over the sidelink interface,
such as vehicle-to-everything (V2X) communication, public safety
(PS) communication, direct file transfer between user devices, and
so on.
[0004] In a sidelink UE-to-network relaying architecture, a relay
UE is served directly by a network node such as an eNB (LTE) or a
gNB (NR), and the relay UE offers service over a sidelink interface
to one or more remote UEs. In some other cases, however, there may
be a need for two UEs to communicate when they do not have direct
visibility to each other over the sidelink interface (for example,
due to being out of range with one another, or due to the
intervention of an obstacle to radio frequency propagation). In
these cases it may be beneficial for a third UE to provide relayed
communication between the first and second UEs. In this situation,
the third UE may be referred to as a relay UE, and the first and
second UEs as remote UEs, endpoint UEs, etc. Such an arrangement
may be described as a UE-to-UE relay (contrasted with a
UE-to-network relay, in which a relay UE provides relaying of
traffic between a remote UE and network infrastructure).
[0005] For UE-to-UE relay, there is a need for a procedure that
allows the remote UEs to initially establish communication with the
relay UE, followed by using the connectivity through the relay UE
to establish a logical connection that allows direct communication
between the remote UEs.
SUMMARY
[0006] A method of connection establishment for UE-to-UE relay in a
cellular communication system is proposed. A sidelink interface is
used for two remote UEs to communicate directly with a relay UE,
and in which the relay UE forwards communications between the
remote UEs to allow end-to-end communication between the remote
UEs. The methods described are applicable to both layer 2 (L2) and
layer 3 (L3) relaying architectures, in which the traffic to be
relayed is carried at either L2 or L3 of a protocol stack. In one
embodiment, a first remote UE initiates a single Direct
Communication (DC) Request that triggers the establishment of
multiple connections between the first remote UE and the relay UE,
and between a second remote UE and the relay UE, such that
end-to-end relayed transport is available between the first and
second remote UE, with hop-by-hop security (that is, security
applied separately to the "first hop" between the first remote UE
and the relay UE and the "second hop" between the second remote UE
and the relay UE). The first and second remote UE can make use of
the end-to-end relayed transport to authenticate and establish
end-to-end secured connection.
[0007] Other embodiments and advantages are described in the
detailed description below. This summary does not purport to define
the invention. The invention is defined by the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 illustrates a wireless cellular communications system
supporting UE-to-UE relay in accordance with a novel aspect.
[0009] FIG. 2 is a simplified block diagram of a wireless
transmitting device and a receiving device in accordance with
embodiments of the current invention.
[0010] FIG. 3 illustrates a layer 2 relaying architecture for
UE-to-UE relay.
[0011] FIG. 4 illustrates a layer 3 relaying architecture for
UE-to-UE relay.
[0012] FIG. 5 illustrates a sequence flow of a first embodiment of
UE-to-UE relay between relay and remote UEs in accordance with one
novel aspect.
[0013] FIG. 6 illustrates a sequence flow of a second embodiment of
UE-to-UE relay between relay and remote UEs in accordance with one
novel aspect.
[0014] FIG. 7 is a flow chart of a method of UE-to-UE relay from
relay UE perspective in accordance with one novel aspect.
[0015] FIG. 8 is a flow chart of a method of UE-to-UE relay from
remote UE perspective in accordance with one novel aspect.
DETAILED DESCRIPTION
[0016] Reference will now be made in detail to some embodiments of
the invention, examples of which are illustrated in the
accompanying drawings.
[0017] FIG. 1 illustrates a wireless cellular communications system
100 supporting UE-to-UE relay in accordance with a novel aspect. 5G
new radio (NR) mobile communication network 100 comprises a 5G core
(5GC) network and a radio access network (not shown) that may
provide cellular service for a plurality of user equipments (UEs)
including UE 101, UE 102, and UE 103. Alternatively, one or more of
UEs 101, 102, and 103 may be out of coverage of a cellular system.
Various cellular systems, including both 4G/LTE and 5G/NR systems,
may provide a facility known as a sidelink interface, which allows
UEs in the system to communicate directly, without the use of any
network infrastructure. The sidelink interface may also be referred
to as a PC5 interface. A variety of applications may rely on
communication over the sidelink interface, such as
vehicle-to-everything (V2X) communication, public safety (PS)
communication, direct file transfer between user devices, and so
on.
[0018] A sidelink interface allows direct device-to-device
communication between UEs. When two UEs that want to communicate
are not in close enough proximity to use the sidelink directly, or
when direct communication between the two UEs is impractical (due
to interference, obstructions, or other factors, for example), they
may rely on a third "relay UE" to route their communications. In
such a situation, the first two UEs may be referred to as remote
UEs, endpoint UEs, and so on. Typically, the endpoint UEs in this
situation cannot detect one another directly but need to rely on
the relay UE to establish communication between them. Thus there is
a need for a procedure that allows the remote UEs to initially
establish communication with the relay UE, followed by using the
connectivity through the relay UE to establish a logical connection
that allows direct communication between the remote UEs. It is
noted that various protocol architectures to support relaying are
possible, and in consequence, the logical connection between the
remote UEs may take various forms, such as a radio resource control
(RRC) connection, a routing path of an internet protocol (IP),
etc.
[0019] For a UE-to-UE relay to operate, a communication path must
be established between the remote UEs via the relay UE. Such a
communication path allows packets of a service to be delivered from
one remote UE to the other remote UE, using the relay UE as an
intermediary. In either a layer-2 (L2) or layer-3 (L3) UE-to-UE
relay architecture, when communication is established between the
remote UEs and the relay UE, there is a need to establish
radio-level connections (for instance, PC5-RRC connections) between
the remote UEs and the relay UE. These radio-level connections
allow management of the protocol layers that terminate between the
relay UE and the remote UEs. In the example of FIG. 1, UE 101 and
UE 102 are two remote UEs, they are also referred to as UE1 and
UE2; and UE 103 is a relay UE, which provides UE-to-UE relay
service for remote UE1 and remote UE2. The PC5-RRC connection 110
between UE1 and the relay UE, and the PC5-RRC connection 120
between UE2 and the relay UE, may be negotiated by direct
signalling over the sidelink interface, but the PC5-RRC connection
130 between UE1 and UE2 must be negotiated using signalling relayed
by the relay UE, since UE1 and UE2 may not have the ability to
communicate directly with one another over the sidelink.
[0020] In accordance with one novel aspect, methods of connection
establishment for UE-to-UE relay are proposed. A sidelink interface
is used for two remote UEs to communicate directly with a relay UE,
which forwards communications between the remote UEs, to allow
end-to-end communication between the remote UEs. The methods
described are applicable to both L2 and L3 relaying architectures,
in which the traffic to be relayed is carried at either L2 or L3 of
a protocol stack. In a preferred embodiment of FIG. 1, remote UE1
first initiates a single Direct Communication (DC) Request message
111, which triggers the establishment of multiple connections
between UE1 and the relay UE and between remote UE2 and the relay
UE, such that end-to-end relayed transport is available between UE1
and UE2, with hop-by-hop security. Finally, UE1 and UE2 make use of
the end-to-end relayed transport to authenticate and establish an
end-to-end secured connection.
[0021] FIG. 2 is a simplified block diagram of wireless devices 201
and 211 in accordance with a novel aspect. For wireless device 201
(e.g., a relay UE), antennae 207 and 208 transmit and receive radio
signal. RF transceiver module 206, coupled with the antennae,
receives RF signals from the antennae, converts them to baseband
signals and sends them to processor 203. RF transceiver 206 also
converts received baseband signals from the processor, converts
them to RF signals, and sends out to antennae 207 and 208.
Processor 203 processes the received baseband signals and invokes
different functional modules and circuits to perform features in
wireless device 201. Memory 202 stores program instructions and
data 210 to control the operations of device 201.
[0022] Similarly, for wireless device 211 (e.g., a remote UE),
antennae 217 and 218 transmit and receive RF signals. RF
transceiver module 216, coupled with the antennae, receives RF
signals from the antennae, converts them to baseband signals and
sends them to processor 213. The RF transceiver 216 also converts
received baseband signals from the processor, converts them to RF
signals, and sends out to antennae 217 and 218. Processor 213
processes the received baseband signals and invokes different
functional modules and circuits to perform features in wireless
device 211. Memory 212 stores program instructions and data 220 to
control the operations of the wireless device 211.
[0023] The wireless devices 201 and 211 also include several
functional modules and circuits that can be implemented and
configured to perform embodiments of the present invention. In the
example of FIG. 2, wireless device 201 is a relay UE that includes
a protocol stack 222, a resource management circuit 205 for
allocating and scheduling sidelink resources, a connection handling
circuit 204 for establishing and managing connections, a traffic
relay handling controller 209 for relaying all or part of control
signalling and/or data traffic for remote UEs, and a control and
configuration circuit 221 for providing control and configuration
information. Wireless device 211 is a remote UE that includes a
protocol stack 232, a relay discovery circuit 214 for discovering
relay UEs, a connection handling circuit 219 for establishing and
managing connections, and a configuration and control circuit
231.
[0024] The different functional modules and circuits can be
implemented and configured by software, firmware, hardware, and any
combination thereof. The function modules and circuits, when
executed by the processors 203 and 213 (e.g., via executing program
codes 210 and 220), allow relay UE 201 and remote UE 211 to perform
embodiments of the present invention accordingly. In one example, a
first remote UE sends an initiating message to a relay UE via the
connection handling circuit, which triggers multiple connections to
be established between the first remote UE and the relay UE and
between the relay UE and a second remote UE. Based on the
established end-to-end relayed transport, an end-to-end secured
connection can be established between the first remote UE and the
second remote UE.
[0025] FIG. 3 illustrates a layer 2 (L2) relaying architecture for
UE-to-UE relay. In the first exemplary protocol stack of FIG. 3,
the relaying operation occurs at the Radio Link Control (RLC)
sublayer of L2. The lower layers of the protocol stack, including a
physical (PHY) layer, a medium access control (MAC) layer, and an
RLC layer, are terminated between the relay UE and each remote UE,
with service data units (SDUs) of the RLC protocol relayed between
the two links at the relay UE. The upper layers of the protocol
stack, including a packet data convergence protocol (PDCP) layer, a
service data adaptation protocol (SDAP) layer in the case of user
plane (UP) operation, and upper layers that may comprise a PC5
radio resource control (PC5-RRC) protocol, a PC5 signalling (PC5-S)
protocol, and/or IP, are terminated end-to-end between remote UE1
and remote UE2. This protocol stack is applicable to both control
and user plane operation, with different upper-layer protocols for
the two cases. In particular, the L2 protocol stack allows for
control and management of a PC5-RRC connection between the two
remote UEs, using the relay UE as a communications intermediary but
without any involvement of the relay UE in the actual protocol
operations for connection control. For example, remote UE1 may send
PC5-RRC messages to remote UE2 (and vice versa) to configure
aspects of a PC5-RRC connection, such as the configuration of the
protocol stack, the configuration of sidelink data radio bearers
(SLRBs or DRBs), and so on.
[0026] FIG. 4 illustrates a layer 3 (L3) relaying architecture for
UE-to-UE relay. In the second exemplary protocol stack of FIG. 4,
the relaying operation occurs at the IP layer of L3. All the
protocol layers (a PHY layer, a MAC layer, an RLC layer, a PDCP
layer, an SDAP layer, and an IP layer) are terminated between the
relay UE and each remote UE, with IP packets relayed at the relay
UE. This allows IP traffic to flow between the remote UEs via the
relay UE, while each radio link is managed separately between the
relay UE and a remote UE. In some examples, the IP addresses of the
remote UEs may be link-local for each of the two radio links and
assigned by the relay UE, with the relay UE performing network
address translation (NAT) to route IP packets to the remote UEs. In
other examples, the IP addresses of the remote UEs may be known to
both remote UEs and routable between the remote UEs, with the relay
UE serving as an IP router.
[0027] In either a L2 or L3 UE-to-UE relay architecture, when
communication is established between the remote UEs and the relay
UE, there is a need to establish radio-level connections (for
instance, PC5-RRC connections) between the remote UEs and the relay
UE. These radio-level connections allow management of the protocol
layers that terminate between the relay UE and the remote UEs. The
PC5-RRC connections between UE1 and the relay UE, and between UE2
and the relay UE, may be negotiated by direct signalling over the
sidelink interface, but the PC5-RRC connection between UE1 and UE2
must be negotiated using signalling relayed by the relay UE, since
UE1 and UE2 may not have the ability to communicate directly with
one another over the sidelink. The basic message flow to setup a
PC5-RRC connection follows the existing art, which results in the
following steps.
[0028] First, an initiating UE sends a Direct Communication (DC)
Request message of a PC5-S protocol to a target UE. Second, the
initiating UE and the target UE exchange messages to authenticate
and establish a security association. Third, the target UE sends a
Direct Communication Accept message to the initiating UE,
completing the setup of a PC5-S connection. Fourth, the initiating
and target UEs automatically consider a PC5-RRC connection to be
established based on the PC5-S connection. In a relaying
environment, where the remote UEs may not have the ability to
communicate directly to one another on the sidelink, none of these
steps can occur between the remote UEs as described above; to
provide connectivity between the remote UEs, the relay UE must
become involved in the communications for connection setup.
[0029] FIG. 5 illustrates a sequence flow of a first embodiment of
UE-to-UE relay between relay and remote UEs in accordance with one
novel aspect. In step 510 of FIG. 5, UE 501 (which will become one
of the remote UEs once a relaying relationship is established)
sends an initiating message, such as a Direct Communication Request
message of a PC5-S protocol. This initiating message may be sent by
broadcast, for example, if an application layer of the initiating
UE did not provide an identifier for the target UE. Alternatively,
the initiating message may be sent by unicast, that is, addressed
specifically to UE 502. The initiating message is received by the
relay UE 503. However, it may not be received by UE 502, for
instance, because of a lack of radio connectivity on the sidelink
interface between UE 501 and UE 502.
[0030] It is noted that in the case where the initiating message is
sent by unicast (addressed to UE 502), the flow of FIG. 5 assumes
that the relay UE 503 knows it should receive and process the
initiating message, even though the message is addressed to UE 502
rather than the relay UE 503. This may be achieved in several ways.
As one example, the relay UE 503 may maintain knowledge of other
UEs in its radio environment that could be considered as remote
UEs, and when it receives the initiating message addressed to UE
502, the relay UE 503 may recognise UE 502 as a candidate remote
UE.
[0031] In step 520 of FIG. 5, the relay UE 503 forwards the
initiating message to UE 502. The forwarded message may maintain
the original transmission mode and addressing from step 510. That
is, if the message in step 510 is sent by broadcast, then the
message in step 520 may also be sent by broadcast; and if the
message in step 510 was sent by unicast, then the message in step
520 may also be sent by unicast. Other information in the message
in step 520 may be modified or appended to indicate that the
message has been relayed. For instance, an identity of the relay UE
503 may be included as a source or a secondary source of the
message, and in case the said identity of the relay UE 503 is a
secondary source of the message, an identity of the primary source
from which the message is relayed i.e. in this case UE 501, is also
included.
[0032] In step 530 of FIG. 5, the relay UE 503 and UE 501 negotiate
authentication and establish a security association. This step may
use the same signalling and procedures as used for general sidelink
communication. In other words, authentication and establishment of
security between the relay UE and UE 501 may not be affected by the
relaying architecture. In step 540 of FIG. 5, the relay UE 503 and
UE 502 negotiate authentication and establish a security
association. This step may likewise use the existing signalling and
procedures.
[0033] In step 550 of FIG. 5, after authentication and security
establishment are complete, the relay UE 503 may determine that it
accepts the establishment of communication with UE 501 and transmit
a response message, for example, a Direct Communication Accept
message of a PC5-S protocol. This step may complete the
establishment of a PC5-S connection between the relay UE 503 and UE
501, and the relay UE 503 and UE 501 may autonomously consider that
a corresponding PC5-RRC connection is established (not shown in the
figure).
[0034] Similarly, in step 560 of FIG. 5, UE 502 may determine that
it accepts the establishment of communication with the relay UE 503
and transmit a response message, for example, a Direct
Communication Accept message of a PC5-S protocol, potentially
resulting in the establishment of a PC5-S connection and a
corresponding PC5-RRC connection between UE 502 and the relay UE.
This determination may take into account said other information in
the message received in step 520 indicating that the message has
been relayed. At this stage, connections are established between UE
501 and the relay UE 503, and between UE 502 and the relay UE 503,
meaning that end-to-end relayed transport is available. However,
security can only be hop-by-hop, meaning that a communication from
UE 501 to UE 502 can be secured (for example, ciphered and/or
integrity-protected) from UE 501 to the relay UE 503, and from the
relay UE 503 to UE 502, but it cannot be secured end-to-end between
UE 501 and UE 502. The relay UE 503 has access to the communication
without security protection, meaning that the relay UE 503 can read
the contents of the communication (since it terminates ciphering)
and/or modify the contents of the communication (since it
terminates integrity).
[0035] After steps 550 and 560 have completed and secure
communication is available between the remote UE 501 and UE 502,
further signalling may occur, for example, to configure the radio
communication layers between the relay UE and the remote UEs. In
one example of a L2 architecture, UE 501 in step 561 may send a
reconfiguration message of a PC5-RRC protocol to the relay UE to
configure the PHY, MAC, and RLC layers of the link between UE 501
and the relay UE. In another example of a L3 architecture, UE 501
in step 561 may send a reconfiguration message of a PC5-RRC
protocol to the relay UE to configure the PHY, MAC, RLC, PDCP, and
SDAP layers of the link between UE 501 and the relay UE.
[0036] It is noted that steps 530/550 and steps 540/560 of FIG. 5
may be asynchronous with one another. In other words, the relay UE
may establish connections with UE 501 and UE 502 independently. For
instance, steps 530 and 540 may overlap in time (in this case the
relay UE would be establishing security with both UE 501 and UE 502
simultaneously). Similarly, step 560 may occur before step 550.
Only when both of steps 550 and 560 have completed will the
end-to-end relayed transport between UE 501 and UE 502 be
available, however. With the end-to-end relayed transport, remote
UE 501 may send a transmission to the relay UE with
addressing/routing information indicating that the transmission is
intended for remote UE 502; remote UE 501 may receive a
transmission from the relay UE with addressing/routing information
indicating that the transmission came from remote UE 502.
[0037] In step 570 of FIG. 5, UE 501 and UE 502 make use of the
end-to-end relayed transport to authenticate and establish security
between them. This step may make use of existing procedures of a
protocol such as a PC5-S protocol. It is noted that the
establishment of security does not require an end-to-end secure
link a priori. Therefore, step 570 can proceed even though, as
noted above, the link between UE 501 and UE 502 (through the relay
UE) only has hop-by-hop security. The messages in step 570 are
transmitted from a remote UE 501 to the relay UE, and forwarded by
the relay UE to the other remote UE 502; however, for purposes of
the figure, the relaying is shown as transparent.
[0038] In step 580 of FIG. 5, UE 502 may determine that it accepts
the establishment of communication and transmit a response message,
for instance, a Direct Communication Accept message of a PC5-S
protocol. Like the messages in step 570, the response message is
forwarded by the relay; that is, it is sent first by UE 502 to the
relay UE 503, and then forwarded by the relay UE 503 to UE 501.
However, for purposes of the figure, the relaying is shown as
transparent. After step 580 has completed, a PC5-S connection is
established between UE 501 and UE 502, with end-to-end secured
transport available for communication between UE 501 and UE 502.
Subsequently, UE 501 and UE 502 may autonomously consider that a
PC5-RRC connection is established between them, and they may use
this PC5-RRC connection for subsequent signalling, such as a
reconfiguration message of a PC5-RRC protocol to configure the
radio layers of the protocol stack for communication between UE 501
and UE 502. For example, in a L2 relaying architecture, UE 501 may
send a reconfiguration message of a PC5-RRC protocol to UE 502 to
configure the PDCP and SDAP layers of the link between UE 501 and
UE 502 (step 581).
[0039] As noted above, configuration of the IP layers of the
connections is outside the scope of the PC5-RRC protocol. If
configuration of the IP layer is required on any of the three
established connections (for example, to allocate IP addresses to
the remote UEs), the flow of FIG. 5 could be expanded to include
additional signalling of a higher-layer protocol such as a PC5-S
protocol. Particularly in a L3 relaying architecture, such
additional signalling might be necessary before relayed transport
is available. For instance, there might be additional PC5-S
signalling between UE 501 and the relay UE after step 550, between
UE 502 and the relay UE after step 560, and/or between UE 501 and
UE 502 after step 580.
[0040] FIG. 6 illustrates a sequence flow of a second embodiment of
UE-to-UE relay between relay and remote UEs in accordance with one
novel aspect. A disadvantage of the flow shown in FIG. 5 is that
the relay UE sets up the PC5-S connection with UE 501 without
knowing if it will successfully establish communication with UE
502. As a result, error cases are possible in which UE 501 and the
relay UE establish a PC5-S connection successfully and communicate
over it, but the relay UE and UE 502 fail to establish a PC5-S
connection (for example, due to a failure of radio connectivity
between them, or due to requirements of other services that make it
impossible for UE 502 to allocate resources for the proposed
service advertised by UE 501). The consequence is a waste of radio
resources for the connection setup between UE 501 and the relay UE,
and an inconvenient requirement to tear down the connection between
UE 501 and the relay UE after setting it up. A message flow that
achieves a similar end-to-end connection setup without this
disadvantage is shown in FIG. 6 as an alternative embodiment.
[0041] FIG. 6 can be seen as a special case of FIG. 5, in which the
signalling between the relay UE and the remote UEs is constrained
to occur in a particular order. In step 610 of FIG. 6, UE 601 sends
an initiating message (e.g., a Direct Communication Request message
of a PC5-S protocol) to the relay UE 603, as in step 510 of FIG. 5.
In step 620 of FIG. 6, the relay UE 603 and UE 601 perform
authentication and establish a security relationship, as in step
530 of FIG. 5. In step 630 of FIG. 6, the relay UE forwards the
initiating message to UE 602, as in step 520 of FIG. 5. In step 640
of FIG. 6, the relay UE 603 and UE 602 perform authentication and
establish a security relationship, as in step 540 of FIG. 5. In
step 650 of FIG. 6, UE 602 sends a response message (e.g., a Direct
Communication Accept message of a PC5-S protocol) to the relay UE
603, as in step 560 of FIG. 5.
[0042] In step 660 of FIG. 6, the flow diverges from FIG. 5, in
that the relay UE 603 waits to send a response message (for
instance, a Direct Communication Accept message of a PC5-S
protocol) to UE 601 until after it has completed the connection
establishment with UE 602. This dependency addresses the deficiency
described above in FIG. 5. If there is a problem in the connection
setup procedure with UE 602, then the relay UE 603 will not finish
setting up the connection with UE 601, since there is no value in
doing so. Rather, it may send a rejection message (for example, a
Direct Communication Reject message of a PC5-S protocol) to UE 601
to indicate that the requested connection will not be set up.
Assuming the relay UE 603 sends the response message as shown in
step 660, steps 670 and 680 of FIG. 6 are the same as steps 570 and
580 of FIG. 5: remote UE 601 and remote UE 602 perform
authentication and establish security, after which remote UE 602
sends a response message (for instance, a Direct Communication
Accept message of a PC5-S protocol) to remote UE 601.
[0043] As a variation on FIG. 6, it is also possible for step 620
to be delayed until after step 650; that is, the relay UE does not
perform authentication and establish security with UE 601 until the
relay UE is sure that it can communicate with UE 602. This approach
has some benefit in efficiency for the failure case, since if the
connection setup with UE 602 fails, the signalling overhead of step
620 can be avoided. However, this variation may also expose the
relay UE to spurious connection attempts from an unauthorised
device in the role of UE 601, which could constitute a low-grade
denial-of-service attack. There is thus a trade-off between
efficiency and the risk of such an attack, and depending on how
likely and how significant the attack scenario is considered,
either the flow of FIG. 6 or the variation with the delayed step
620 might be preferable in a real deployment.
[0044] FIG. 7 is a flow chart of a method of UE-to-UE relay from
relay UE perspective in accordance with one novel aspect. In step
701, a relay UE receives a first communication request message from
a first remote UE. The relay UE offers relay service between the
first remote UE and a second remote UE. In step 702, the relay UE
sends a first response message to the first remote UE and thereby
establishing a first connection of a first protocol layer with the
first remote UE. In step 703, the relay UE sends a second
communication request message to a second remote UE in response to
the receiving the first communication request message. In step 704,
the relay UE receives a second response message from the second
remote UE and thereby establishes a second connection of the first
protocol layer with the second remote UE. In step 705, the relay UE
receives at least one transmission on the second connection from
the second remote UE. In step 706, the relay UE forwards the at
least one transmission to the first remote UE on the first
connection.
[0045] FIG. 8 is a flow chart of a method of UE-to-UE relay from
remote UE perspective in accordance with one novel aspect. In step
801, a remote UE sends a first communication request message to a
relay UE that offers relay service between the first remote UE and
the second remote UE. In step 802, the remote UE receives a first
response message from the relay UE and thereby establishes a first
connection of a first protocol layer with the relay UE. In step
803, the remote UE communicates with a second remote UE via the
relay UE. In step 804, the remote UE receives a second response
message from the second remote UE. The second response message is
triggered by and in response to the first communication request
message via the relay UE. In step 805, the remote UE establishes a
second connection of the first protocol layer with the second
remote UE.
[0046] Although the present invention has been described in
connection with certain specific embodiments for instructional
purposes, the present invention is not limited thereto.
Accordingly, various modifications, adaptations, and combinations
of various features of the described embodiments can be practiced
without departing from the scope of the invention as set forth in
the claims.
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